This invention relates to the production of a desirable fluid (e.g., oil, gas, water, etc.) from a subterranean formation, and more particularly to a method for reducing undesirable fluid production from a producing well penetrating the formation or another formation or formations penetrated by the producing well.
In one application, the desirable fluid is water that is useful for personal, municipal, or commercial use, and the undesirable fluid is water not valuable for the same use. An example of this application is a well penetrating one formation containing potable water and another formation containing brackish water.
In another application, the desirable fluid is water that contains a commercially valuable concentration of one or more chemical species, and the undesirable fluid is water without the commercially-valuable concentration. An example of this application is a well penetrating one formation that contains water with a commercially-valuable bromide ion concentration and another formation containing water without a sufficient bromide ion concentration.
In still another application, the desirable fluid contains a commercially-valuable gas concentration, and the undesirable fluid does not. An example of this application is a well penetrating one formation that contains a commercially-valuable concentration of carbon dioxide and another formation containing fluid without sufficient carbon dioxide.
In yet another application, the desirable fluid contains a commercially-valuable hydrocarbon concentration and the undesirable fluid is water without a hydrocarbon concentration sufficient for commercial use. An example of this application is a well penetrating one formation containing a fluid with a commercially-valuable concentration of oil and a portion of the formation or another formation penetrated by the well containing water without a commercially-valuable concentration of oil. As will be appreciated by one of ordinary skill in the art, the hydrocarbon can be oil, gas, or any mixture thereof.
As will be appreciated by one of ordinary skill in the art, the desirable fluid can contain any desirable product extracted from subterranean formations through wells, or a mixture of any of these desirable products. As will also be appreciated by one of ordinary skill in the art, different portions of a single subterranean formation can contain one or more desirable fluids and one or more undesirable fluids. As will also be appreciated by one of ordinary skill in the art, desirable fluids can occur in multiple subterranean formations intersected by a well, and undesirable fluids can occur in many other subterranean formations intersected by the well that lie between the subterranean formations containing the desirable fluids.
In a water-drive reservoir, the predominant mechanism which forces the movement of desirable fluid in the reservoir toward the wellbore is the advancement of a formation water aquifer. The formation water phase is found beneath the hydrocarbon phase in a bottom-water, hydrocarbon-beating reservoir or on the outer flanks of the hydrocarbon column in an edge-water, hydrocarbon-bearing reservoir. In a water-flooded reservoir, water is injected into the formation in water injection wells, forcing the movement of desirable fluids toward the producing well. In these cases, water moves into the reservoir pore spaces which were once filled with desirable fluids in response to continued production of the desirable fluids. Over time, this water movement leads to the advancement of water into the producing zone of the wellbore and the well eventually begins to produce undesirable quantities of water. The ever increasing production rate of water is undesirable in hydrocarbon-producing wells and eventually makes the wells uneconomical to operate. There has been a continuing need for an economical and effective method for reducing or virtually eliminating the water production from such wells.
In a gas-cap-expansion reservoir the predominant mechanisms which force the movement of desirable fluid toward the wellbore are the expansion of an overlying gas cap and the effect of gravity. In a hydrocarbon-bearing reservoir, oil and dissolved gas are found beneath the gas cap. In a gas-flooded reservoir, gas is injected into the formation in gas injection wells, forcing the movement of desirable fluids toward the producing well. In these cases, gas moves into the reservoir pore spaces which were once filled with desirable fluids in response to continued production of the desirable fluids. Over time, this gas movement leads to the advancement of undissolved gas into the producing zone of the wellbore and the well eventually begins to produce undesirable quantities of undissolved gas. This is undesirable because it reduces the desirable fluid production capacity of the well and inefficiently uses the energy of the expanding gas cap or the injected gas to move the desirable fluid toward the well. There is a need for a method to reduce or eliminate the undissolved gas production from such wells.
In combination-drive reservoirs, the effects of water-drive and gas-cap-expansion can both occur. In this type reservoir, an edge-water or bottom-water-drive combines with the effect of an expanding gas cap to force desirable fluid toward the production well. There is a need for an economical and effective method to shut off undesirable, undissolved gas production and water production in these type reservoirs.
Separate reservoirs are often found vertically stacked in adjacent formations, often referred to as layers (i.e., multi-layered reservoirs). To extract the desirable fluids from these multi-layered reservoirs in the most economical manner, single boreholes are often used to simultaneously extract fluids from multiple reservoirs. The region where the borehole intersects one of these reservoirs is referred to as a production zone. A single zone can have more than one fluid-producing region, referred to as intervals. The reservoirs usually have unique fluid properties, geologic properties, and production drive mechanisms. In these reservoirs, it is sometimes necessary to shut off undesirable fluid production in a location in the borehole that is intermediate between two desirable fluid-productive intervals, with the two desirable fluid-productive intervals usually in different zones.
In producing wells, there is the common occurrence of unconsolidated sandstone reservoir rock formations. In this type of formation, sand grains which make up the sandstone rock do not contain adequate inter-granular cementation or rock strength to ensure rock stability during the production of fluids. As a result, the rock in its natural state often fails when subjected to the stresses imposed on it during fluid production. Small rock fragments are then produced into the wellbore. Once accumulated in the wellbore, the low permeability of this fine grain material restricts the productivity of the adjacent formation and deeper portions of the formation.
Various techniques to increase the stability of the sandstone reservoir rock (i.e., methods of sand control) have been employed. One such method is commonly referred to as "gravel packing." In a typical gravel-packed well, one or more perforated joints of production tubing are wrapped with screen. The wrapped section of production tubing is located adjacent a producing zone. Uniformly sized and shaped sand grains (i.e., "gravel") are placed (i.e., "packed") in a wellbore's perforations and in the annular volume between the well's production casing and the screen surrounding the production tubing. The sand grains, or "gravel", are packed tightly together and sized as large as possible while still restricting the formation sand from moving into the gravel. The openings in the screen around the production tubing are sized as large as possible while still restricting the gravel from passing through the openings. In this way, productivity is kept as high as possible while preventing formation sand and gravel from entering the tubing. The screen is normally placed between two packers which contains the sand in an area adjacent to the producing zone. As the well is produced, undesirable fluid moves into the producing zone and remedial measures which isolate the undesirable fluid from the production tubing are necessary.
One known method of isolating an undesirable fluid-producing interval within the production zone is to dump cement into the wellbore. There are several problems with the use of cement for this purpose. First, when cement is dump bailed into the wellbore, a malfunction of the bailer can inadvertently bridge off cement in the unperforated (i.e., blank) area of the tubing above the gravel-packed region. The cement must then be drilled out to clear the tubing. Second, if the cement formulation is not correct, the cement may not completely penetrate the perforated tubing and may fail to block off channels between the tubing and the gravel-pack screen. Third, even if the cement effectively blocks the channels between the tubing and the screen, undesirable fluid still flows vertically through the gravel-packed annulus. Another known method of isolating an undesirable fluid-producing interval within the production zone is to convey an obstruction near the base of the desirable fluid-producing interval using regular tubing or a coiled tubing, and then pump a plugging material below the obstruction using regular tubing or coiled tubing as a conduit for the plugging material. It is not known to release a plugging material below an obstruction without using regular tubing or coiled tubing. Also, it is not known to pump a buoyant plugging material.
Another known procedure is disclosed in U.S. Pat. No. 4,972,906 issued to McDaniel. This procedure involves delivering a mixture of a liquid epoxy material and a hardener for the epoxy material to a gravel-packed region to seal off the production of water. The mixture of liquid epoxy material and hardener is characterized in that the epoxy material has a density greater than the density of the well fluids. The first step of the process is to ensure that the well remains essentially dormant (i.e., there is no downhole fluid movement or "crossflow") during the process so that the epoxy is not dispersed into portions of the well which do not require plugging. Also, the epoxy plug can become "honeycombed" if formation fluid continues to trickle into the wellbore before the epoxy is completely hardened. The epoxy material and hardener is dumped in the production tubing in an amount sufficient to form a solid plug from the bottom of the production tubing up to a point slightly above the water interval. In a gravel-packed well, the plug fills the perforated tubing, the screen, and the gravel, and may enter the perforations in the water-producing interval to plug off production of water from the zone. This procedure can be effective but presents problems when the interval to be isolated is long or when there is open casing below the gravel-pack. In either case, a large amount of epoxy is required.
U.S. Pat. No. 5,090,478 issued to Summers discloses a method for reducing water production from a gravel-packed well. The water encroachment interval of a gravel-packed, hydrocarbon-producing well is isolated by placing a plug in the perforated tubing below the hydrocarbon-producing interval, then placing two sand layers on the plug in the perforated tubing. The first sand layer is made up of sand which is coarser than the sand in the gravel pack. This coarse sand bridges off in the channels between the perforated tubing and the gravel-pack screen. The second sand layer is made up of sand which generates a tight matrix in the perforated tubing. A liquid resin is placed on top of the second sand layer. The resin preferentially flows outward into the gravel pack. However, the resin does not form an actual flat disk because some of the resin moves downward somewhat through the gravel, as well as down the channels between the screen and the perforated tubing. The resulting disk-like layer of resin prevents further production of water from the encroaching water interval. One limitation of this method is that water can flow out of the perforated tubing and up through the gravel and/or the formation and back into the perforated tubing (i.e., "crossflow") above the resin plug before the plug has hardened and leave open flow channels through the resin.
In view of the limitations of the known devices, it is an object of the present invention to provide methods for reducing or eliminating undesirable fluid production from a producing well. It is a further object of this invention to provide methods for reducing or eliminating undesirable fluid production that are effective in a wellbore that experiences "crossflow". It is also an object of this invention to provide methods for reducing or eliminating undesirable fluid production that are cost-effective, reliable, and easily reversible.